Quality Control of Waste Waters and Surface Waters

The Subotica Waterworks and Sewerage PUC’s laboratory for waste water quality control is located within the Waste Water Treatment Plant (WWTP). There are two organisational units within it: the chemical and the biological laboratories. The Laboratory is equipped with the devises and equipment for physical, chemical and hydro-biological analyses though there are real needs for more sophisticated instruments, too. The qualified personnel has huge experience in this kind of work, in water analyses and treatment.

The Laboratory continuously controls the quality of industrial and communal wastewaters, the quality of surface waters and the water of the Lake Palic recipient. The Laboratory makes systematic controls of the waste water treatment installations , whereas it covers all phases of treatment from the inlet of raw wastewater to the discharge of treated one, and also controls the bio-active sludge.

Raw wastewaters are waters entering the waste water plant, composed of the waste waters of households, corporate entities and institutions and underground and stormwater channelled to or entering the WWTP.

Plant analyses are made on a daily basis for treatment technology management needs. Analyses cover grab and composite samples of water and sludge Composite samples are prepared from a series of grab samples, mostly from samples collected over one day, i.e. 24 hours with two to three hours apart sampling schedule.

There are also systematic and more detailed weekly, monthly and quarterly analyses controlling the operation of the WWTP, monitoring the treated water quality in the recipient, of the surface waters and monitoring the quality of industrial, technological waste waters, of the sewerage water quality and outsourced services.

A lion’s share in the works done in 2006 belonged to the analyses of water and sludge quality monitoring for the needs of the WWTP in Subotica.

Waste Water Chemical Analysis in 2006

The Waste Waters of Companies in Subotica

A total of 127 samples taken from industrial consumers were analysed. The deviances of the discharged waste water from the prescribed values are determined on the base of maximum permitted concentration (MPC) laid down in Article 18 of the Decision on Public Sewerage (Subotica Municipal Official Journal no. 39/2001).

Based on the assessments of waste water quality in relation to the set criteria, the largest organic pollution was recorded in Mlekara (Dairy) and Fidelinka (Starch Production Plant), while inorganic pollution dropped since the chemical industry and leather factory have stopped their operations.

The waste water quality of monitored industrial polluters has not met the requirements for discharging their waste waters in the city sewerage, due to the reasons as follows:

REMARK: The above list corresponds with the ranking of polluters.

There are two methods to arrange the polluters ranking. One is made on the base of the average pollution concentration expressed in mg/l, while the other is made based on mass balance expressed in kg/month. The ranking of polluters varies in the two lists made on these principles. The Decision on Public Sewerage laid down the MPC limits (mg/l) of the waste water, and the size of deviation from the MPC gives the ranking of polluters.

For the WWTP, mass balance bears higher importance, since besides pollution concentration it also takes into account the quantity of the emitted waste water in a certain time period.

The quality of waste waters emitted by controlled polluters frequently fails to fulfil the requirements of discharging waste waters in the public sewerage as set by the municipal Decision on Public Sewerage.

According to the polluters list made on the base of mass balance, the Dairy is on the first place in view of emitting organic matters and grease, but also with respect to the emission of total nitrogen and phosphor.

In the waste waters discharged by the Starch Producing Plant sedimentary organic matter has been significantly decreased compared to prior years, but dissolved organic matters keep to be high.

Panonija, the leather factory was out of operation during the whole year.

The pollutions by the Fidelinka Starch Production Plant and the Dairy had negatively affected the WWTP, since they present an additional load to the plant, more power is needed for their treatment and cause disturbances in separating the treated water and the bio-active sludge.

The WWTP operates continuously at full capacity. The Plant is hydraulically loaded, and sometimes it is biologically overloaded. Result analyses show that the concentration of inlet organic load has been decreased if compared to the previous year. The set level of treatment for 2006 based on decreasing BPK5, was 92% in average.

The quality of the treated waste water meets the foreseen norms at mechanical and biological treatment. In the lagoon system self-cleaning is almost non-existent.

The Biological Quality Control of Wastewaters, Surface Waters and Bioactive Sludge

Basic Activities

The Biological Laboratory makes the toxicological analyses of industrial and surface waters, as well as the analyses of enzyme (phosphatase) activities of the inlet and outlet waste water at WWTP Subotica and Palic, and of the surface waters (lagoon systems, fish ponds, Lake Palic, Lake Omladina, Lake Ludas and the Kires stream).

Most of the laboratory work covers the microscopic analysis of sludge made daily on sludge samples taken from the aeration lagoons 1 and 2 and the recirculation sludge.

Toxicological Analyses

Toxicity level is determine by a standard, short-term (24h) test in aquarium fish Lebistes reticautus. LC-50 (the concentration of a chemical which kills 50% of a sample population) is determined. Results are expressed in % Tlm (median tolerance limit-conversely proportional to toxicity level) or Dil.Tlm (indicates the number of times the water is to be diluted in order to achieve LC-50). If the %Tlm is lower (>100), the toxicity of the analyzed sample is higher.

The Biochemical Analysis of Phosphatase Activity

The index of phosphatase activity index is a rapid and fairly reliable indicator of total microbiological activities in water (which indirectly indicates the organic load of the water).

Bacteriological Analyses

Especially from the ecological point of view, bacteriological analyses are useful sources of information about the status of the eco-systems of water and the biological purification of the water. In 2006, a laminar chamber (for sterile planting of cultures) and a thermostat with cooling option (for maintaining temperatures lower than room temperature) were purchased, thus the technical condition of introducing and systematizing these analyses have been created.

Microscopic Active Sludge Analyses

Microscopic sludge tests include analyses of native, fresh preparations of sludge and status assessment in the system based on the quality of flocculi and the composition of micro-organisms. By colouring and identifying filamentous (rod-shaped) bacteria (which became dominant in the sludge after the transfer to deep aeration system), and through an experimental approach to find the conditions unfavourable for their growth and development, and by applying the obtained results in the technology, the due and effective combating of their proliferation and the floating of sludge floccules on the surface from sedimentary tanks were achieved. The purchase of a digital camera with software for photo-processing and its connection to a PC equipment (also a new one) has significantly facilitated and enhanced the quality of the laboratory’s work and includes an advanced use and handling of the electronic database.

The currently applied methodology in the work with active sludge, the data base and processing, digital photographing and software processing, experience and knowledge gained over the last 2-3 years, rank this Laboratory among the leading ones in the country, while the standard methods of works are good fundaments for comparison and building contacts with other laboratories from abroad.

In 2006, the first results (since the existence of the Laboratory) of the active sludge biological analyses were published (on the international conferences: "Waste Waters, Communal Solid Waste and Hazardous Waste" and " The Ecological Truth”)… Details

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The Biological Quality Control of Wastewaters, Surface Waters and Bioactive Sludge